Text lesson

Unit 1 — Chemical Reactions and Their Environmental Impacts

Science — Third Preparatory

2.3 Ignition point and flammability

Take two identical paper strips, one dry and one wet.
Hold each, in turn, 2 cm above the tip of a candle flame and time how long until it catches fire.
The dry strip ignites fast.
The wet one does not burn easily because the water absorbs the heat of the flame and delays the paper from reaching its ignition temperature.
(Safety wear goggles and heat-resistant gloves; work on a stable heat-resistant board away from flammable objects; have an extinguisher available.)

Comparison aspect	Main idea	Example	Keywords
Ignition point	is the lowest temperature to a material must be heated so that it starts burning and continues to burn by itself	—	lowesttemperaturematerialmust
Flammability	expresses how easily and quickly a substance ignites at the surrounding temperature. Substances with a low ignition point	petrol and alcohol are highly flammable and their containers carry warning signs	expresseseasilyquicklysubstance
This answers the forest question	thin dry leaves have a large surface area and little mass so they heat up and reach their ignition point quickly a thick branch takes much longer to heat to that temperature	—	thinleaveslargesurface

Unit 1 — Chemical Reactions and Their Environmental Impacts · 11 / 30

2.3 Ignition point and flammability